LM2703MF-ADJ

LM2703 NSC | Alldatasheet

Document overview

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Technical content

Features

n 350mA, 0.7Ω, internal switch n Uses small surface mount components n Adjustable output voltage up to 20V n 2.2V to 7V input range n Input undervoltage lockout n 0.01µA shutdown current n Small 5-Lead SOT-23 package

Applications

Typical Application Circuit 20030601 FIGURE 1. Typical 20V Application

TJmax = 125˚C,θJA = 220˚C/W(Note 2)

Ordering Information

Order Number Package Type NSC Package Drawing Top Mark Supplied As LM2703MF-ADJ SOT23-5 MA05B S48B 1000 Units, Tape and Reel LM2703MFX-ADJ SOT23-5 MA05B S48B 3000 Units, Tape and Reel Pin Description/Functions Pin Name Function 1 SW Power Switch input. 2 GND Ground. 3 FB Output voltage feedback input.

4 SHDN

Shutdown control input, active low. 5V IN Analog and Power input. SW(Pin 1): Switch Pin. This is the drain of the internal NMOS power switch. Minimize the metal trace area con- nected to this pin to minimize EMI. GND(Pin 2): Ground Pin. Tie directly to ground plane. FB(Pin 3):Feedback Pin. Set the output voltage by selecting values for R1 and R2 using: Connect the ground of the feedback network to an AGND plane which should be tied directly to the GND pin. SHDN(Pin 4):Shutdown Pin. The shutdown pin is an active low control. Tie this pin above 1.1V to enable the device. Tie this pin below 0.3V to turn off the device. VIN(Pin 5):Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. LM2703 www.national.com 2

Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. V IN 7.5V SW Voltage 21V FB Voltage 2V SHDN Voltage 7.5V Maximum Junction Temp. TJ (Note 2) 150˚C Lead Temperature (Soldering 10 sec.) 300˚C Vapor Phase (60 sec.) 215˚C Infrared (15 sec.) 220˚C ESD Ratings (Note 3) Human Body Model Machine Model (Note 4) 2kV 200V Operating Conditions Junction Temperature (Note 5) −40˚C to +125˚C Supply Voltage 2.2V to 7V SW Voltage Max. 20.5V

Electrical Characteristics

Specifications in standard type face are for TJ = 25˚C and those inboldface type apply over the fullOperating Temperature Range (TJ = −40˚C to +125˚C). Unless otherwise specified. VIN =2.2V. Symbol Parameter Conditions Min (Note 5) Typ (Note 6) Max (Note 5) Units IQ Device Disabled FB = 1.3V 40 70 µADevice Enabled FB = 1.2V 235 300 Shutdown SHDN = 0V 0.01 2.5 VFB FeedbackTrip Point 1.189 1.237 1.269 V ICL Switch Current Limit 275 260 350 400 400 mA IB FB Pin Bias Current FB = 1.23V (Note 7) 30 120 nA VIN Input Voltage Range 2.2 7.0 V RDSON Switch RDSON 0.7 1.6 Ω TOFF Switch Off Time 400 ns ISD SHDN Pin Current SHDN = VIN,T J = 25˚C 08 0 nASHDN = VIN,T J = 125˚C 15 SHDN = GND 0 IL Switch Leakage Current V SW = 20V 0.05 5 µA UVP Input Undervoltage Lockout ON/OFF Threshold 1.8 V V FB Hysteresis Feedback Hysteresis 8 mV SHDN Threshold SHDN low 0.7 0.3 VSHDN High 1.1 0.7 θJA Thermal Resistance 220 ˚C/W Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance,θJA, and the ambient temperature, TA. See the Electrical Characteristics table for the thermal resistance. The maximum allowable power dissipation at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) −T A)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. Note 4: ESD susceptibility using the machine model is 150V for SW pin. Note 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% production tested or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 6: Typical numbers are at 25˚C and represent the most likely norm. Note 7: Feedback current flows into the pin. LM2703 www.national.com3

Typical Performance Characteristics Enable Current vs VIN (Part Switching) Disable Current vs VIN (Part Not Switching) 20030605 20030606 Efficiency vs Load Current Efficiency vs Load Current 20030610 20030611 LM2703 www.national.com 4

Typical Performance Characteristics (Continued) Efficiency vs Load Current SHDN Threshold vs V IN 20030612 20030613 Switch Current Limit vs VIN Switch RDSON vs VIN 20030614 20030615 LM2703 www.national.com5

Typical Performance Characteristics (Continued) FB Trip Point and FB Pin Current vs Temperature Output Voltage vs Load Current 20030623 20030622 Step Response Start-Up/Shutdown 20030616 VOUT = 20V, VIN = 2.5V 1) Load, 1mA to 10mA to 1mA, DC 2) V OUT, 200mV/div, AC 3) IL, 200mA/div, DC T = 50µs/div 20030617 VOUT = 20V, VIN = 2.5V 1) SHDN, 1V/div, DC 2) IL, 200mA/div, DC 3) VOUT, 20V/div, DC T = 400µs/div R L = 1.8kΩ LM2703 www.national.com 6

Operation (Continued) The LM2703 features a constant off-time control scheme. Operation can be best understood by referring toFigure 2 and Figure 3. Transistors Q1 and Q2 and resistors R3 and R4 ofFigure 2form a bandgap reference used to control the output voltage. When the voltage at the FB pin is less than 1.237V, the Enable Comp inFigure 2enables the device and the NMOS switch is turned on pulling the SW pin to ground. When the NMOS switch is on, current begins to flow through inductor L while the load current is supplied by the output capacitor C OUT. Once the current in the inductor reaches the current limit, the CL Comp trips and the 400ns One Shot turns off the NMOS switch.The SW voltage will then rise to the output voltage plus a diode drop and the inductor current will begin to decrease as shown inFigure 3. During this time the energy stored in the inductor is transferred to C OUT and the load. After the 400ns off-time the NMOS switch is turned on and energy is stored in the inductor again. This energy transfer from the inductor to the output causes a stepping effect in the output ripple as shown inFigure 3. This cycle is continued until the voltage at FB reaches 1.237V. When FB reaches this voltage, the enable compara- tor then disables the device turning off the NMOS switch and reducing the Iq of the device to 40uA. The load current is then supplied solely by C OUT indicated by the gradually decreasing slope at the output as shown inFigure 3. When the FB pin drops slightly below 1.237V, the enable compara- tor enables the device and begins the cycle described pre- viously. The SHDN pin can be used to turn off the LM2703 and reduce the Iq to 0.01µA. In shutdown mode the output voltage will be a diode drop lower than the input voltage.

Application Information

The appropriate inductor for a given application is calculated using the following equation: where VD is the schottky diode voltage, ICL is the switch current limit found in theTypical Performance Characteris- tics section, and TOFF is the switch off time. When using this equation be sure to use the minimum input voltage for the application, such as for battery powered applications. For the LM2703 constant-off time control scheme, the NMOS power switch is turned off when the current limit is reached. There is approximately a 200ns delay from the time the current limit is reached in the NMOS power switch and when the internal logic actually turns off the switch. During this 200ns delay, the peak inductor current will increase. This increase in inductor current demands a larger saturation current rating for the inductor. This saturation current can be approximated by the following equation: Choosing inductors with low ESR decrease power losses and increase efficiency. Care should be taken when choosing an inductor. For appli- cations that require an input voltage that approaches the output voltage, such as when converting a Li-Ion battery voltage to 5V, the 400ns off time may not be enough time to discharge the energy in the inductor and transfer the energy to the output capacitor and load. This can cause a ramping effect in the inductor current waveform and an increased ripple on the output voltage. Using a smaller inductor will cause the I PK to increase and will increase the output voltage ripple further. This can be solved by adding a 4.7pF capaci- tor across the R F1 feedback resistor (Figure 2) and slightly increasing the output capacitor. A smaller inductor can then be used to ensure proper discharge in the 400ns off time. DIODE SELECTION To maintain high efficiency, the average current rating of the schottky diode should be larger than the peak inductor cur- rent, I PK. Schottky diodes with a low forward drop and fast switching speeds are ideal for increasing efficiency in por- table applications. Choose a reverse breakdown of the schottky diode larger than the output voltage. CAPACITOR SELECTION Choose low ESR capacitors for the output to minimize output voltage ripple. Multilayer ceramic capacitors are the best choice. For most applications, a 1µF ceramic capacitor is sufficient. For some applications a reduction in output volt- age ripple can be achieved by increasing the output capaci- tor. Local bypassing for the input is needed on the LM2703. Multilayer ceramic capacitors are a good choice for this as well. A 4.7µF capacitor is sufficient for most applications. For additional bypassing, a 100nF ceramic capacitor can be used to shunt high frequency ripple on the input. LAYOUT CONSIDERATIONS The input bypass capacitor C IN, as shown inFigure 1, must be placed close to the IC. This will reduce copper trace resistance which effects input voltage ripple of the IC. For additional input voltage filtering, a 100nF bypass capacitor can be placed in parallel with C IN to shunt any high fre- quency noise to ground. The output capacitor, COUT, should also be placed close to the IC. Any copper trace connections for the Cout capacitor can increase the series resistance, which directly effects output voltage ripple. The feedback network, resistors R1 and R2, should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the feed- back resistor network should connect directly to an analog ground plane. The analog ground plane should tie directly to the GND pin. If no analog ground plane is available, the ground connection for the feedback network should tie di- rectly to the GND pin. Trace connections made to the induc- tor and schottky diode should be minimized to reduce power dissipation and increase overall efficiency. LM2703 www.national.com 8

FIGURE 7. 5V to 12V Application

Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead Small Outline Package (M5) For Ordering, Refer to Ordering Information Table LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Fax: +65-6250 4466 Email: ap.support@nsc.com Tel: +65-6254 4466 National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560 www.national.com LM2703 Micropower Step-up DC/DC Converter with 350mA Peak Current Limit National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.